While a number of recent efforts are being made to achieve a finer pattern rule in the drive for higher integration and operating speeds in LSI devices, deep-ultraviolet lithography is thought to hold particular promise as the next generation in microfabrication technology. Deep-UV lithography is capable of achieving a feature size of 0.5 μm or less and, when a resist having low light absorption is used, can form patterns with sidewalls that are nearly perpendicular to the substrate.
Recently developed acid-catalyzed chemical amplification positive resists, such as those described in JP-B 2-27660, JP-A 63-27829, U.S. Pat. No. 4,491,628 and U.S. Pat. No. 5,310,619, utilize a high-intensity KrF excimer laser as the deep-UV light source. These resists, with their excellent properties such as high sensitivity, high resolution, and good dry etching resistance, are especially promising for deep-UV lithography.
Such chemically amplified positive resists include two-component systems comprising a base resin and a photoacid generator, and three-component systems comprising a base resin, a photoacid generator, and a dissolution inhibitor having acid labile groups.
For example, JP-A 62-115440 describes a resist material comprising poly-p-tert-butoxystyrene and a photoacid generator. JP-A 3-223858 describes a similar two-component resist material comprising a resin bearing tert-butoxy groups within the molecule, in combination with a photoacid generator. JP-A 4-211258 describes a two-component resist material which is comprised of polyhydroxystyrene bearing methyl, isopropyl, tert-butyl, tetrahydropyranyl, or trimethylsilyl groups, together with a photoacid generator.
JP-A 6-100488 discloses a resist material comprised of a polydihydroxystyrene derivative; such as poly[3,4-bis(2-tetrahydropyranyloxy)styrene], poly[3,4-bis(tert-butoxycarbonyloxy)styrene] or poly[3,5-bis(2-tetrahydropyranyloxy)styrene], and a photoacid generator.
The base resins in these resist materials have an optimum baking temperature as high as about 130° C. when the acid labile group is tert-butyl, and low resolution when the acid labile group is tert-butoxycarbonyl. In either case, the resist pattern tends to take on a T-top profile. By contrast, when the acid labile groups are alkoxyalkyl groups such as ethoxyethyl and 2-tetrahydropyranyl which are cleaved by weak acids, the corresponding resins have the drawback that the pattern configuration is considerably narrowed with the passage of time between exposure and heat treatment. This makes it difficult to form a resist film to a reduced thickness compliant with a reduced feature size. Also some resins have poor heat resistance so that lenses in the stepper can be contaminated by outgassing from within the resist during development. Because of these problems, none of the foregoing resins are compliant with micro-patterning.
To provide higher transparency and firm adhesion to substrates and to improve footing on substrates and etching resistance, JP-A 3-275149 and JP-A 6-289608 propose resist materials using copolymers of hydroxystyrene with a (meth)acrylic acid tertiary ester. The resist materials of this type are not satisfactory because of poor heat resistance and an indefinite pattern profile after exposure.
Also developed was a resist composition comprising an indene-(meth)acrylic acid tertiary ester copolymer as described in JP-A 2002-202610. Since the copolymer has acid labile groups of the acetal type as is often the case in the prior art, a problem can occur that a pattern profile degrades as a result of the pattern film becoming thinner.
With the current trend toward higher resolution, thinning of pattern film is in simultaneous progress. Accordingly, there is a desire to have a resist material having a definite resist pattern profile after development and higher etching resistance.